Power line signaling



March 19, 1929.

Lyw. DAVEE Powma LINE SIGNALING Filed Feb. 9,"192'1 5 Sheets-Sheet l March 19, 1929. 1 W. DAVEE POWER LINE SIGNALING Filed Feb. 9, 1927 5 Sheets-Sheet 2 :C: n r L STAT/0N AP6/NAL March 19, 19.29. L.. W. DAVEE POWFRA LINE SIGNALING Filed Feb. 9, 1927 5 Sheets-Sheet 4 March 19, 1929. W, D'AVEE @$705,903

POWER LINE SIGNALING Filed Feb, 9, 192'? 5 Sheets-Sheet 5 f2; Je.

Patented Mar. 19, i929.

UNITED v smrrs LABORATORIES,INcORrORATED, OF NEW YORK, N. Y., A CORPORATION or NEWA YORK.

Prvrrzia'r4 l OFFICE.

"LAWRENCE W, 'BAYER OF BROOKLYN,` NEW YORK, As'sI'GNoR To BEI-.L TELEPHONE POWER LINE SIGNALING.'

Application. 1in-,a rbruay 9, 1927. serial No. 166,863.

This invention relates to communication by means of carrier frequency w ves and'particularly to communication o er composite power current and carrier wave transmission 'systems employing repeaters.

An object of t-he invention is to increase I theutility and efficiency of power line signaling systems employing repeaters.

A related object of the invention is to reduce the communication channels which may be lost to service due to the failure of 'a portion of the transmission circuit.'

The invention is especially applicable' to power line signaling systems of the type disclosed in 'a copending application of W. V.

Wolfe, Serial No. 166,664, filed 4 February 8,

l927, in which any of a plurality Of stations may call and converse with any other station on the line. A feature of the present invention consist-s in effecting communication between stations located on 'the same side of' a break occurring in the transmission circuit.v In an important embodiment of the invention means are provided for communicating between stations located on the same side of a repeater when the repeater is lost to service.

lin the'system disclosed inthe above mentionedWolfe application, a repeater is employed to repeat calling impulses and telephone conversations between stations located on either side of a discontinuity inthe power line, such as a voltage transformer o r an open power switch. 'Three different carrier frequencies are utilized to communicate selectively betweenstations on the same side of the repeater, lbetween any station and the repeater, and between stations on lopposite sides of the repeater. Any station desiring to call another station transmits properly arranged groups of carrier impulses of one frequency which are received only by the repeater. The carrier impulses received by the repeater are converted into carrier impulses of another frequency whichv ai'e impressed upon the power line on both sides of the repeater. These impulses Operate a selector at the called station which is adjusted to respond to that particular group of impulses. Thus, even lthough the calling station and the called station are on the same side of the repeater, the impulses transmitted by the calling station must be converted at the repeater into impulses of a frequency .receivable at the called station. -If the repeater is rendered inoperativefor any reason, th`e entire signaling system is lost toservice until the nec'essary repairs are made. Likewise, if a break occurs in the line on one side of the repeater,

all stations on that side of the repeater are rendered inoperative.

Inthe system of the present invention calling is normally accomplished in the manner disclosed in the l/Volfe application'. That is,

connection between ,any two stations is normally effected through the repeater. Accord'- ing to a feature of the invention, however,

means are provided for communicating b etween terminals located on the same side of a break in the line, or on the same side of the.

repeater,l if the repeaterffails to operate.

This is accomplished by means of a switching arrangement at each station whereby the transmitting apparatus may be converted to A transmit calling impulses of afrequency which is receivable by all stations located on lthe same side of the repeater. This switching arrangement is operated only at the station originating the call, and isemployed only when it has been determined that the repeater will not receive the calling impulses.

The various features and advantages of the invention will be described in `detail in connection with the accompanyingdrawings,

Figs. l to 4, inclusive, illustrate diagram-- matically a power line signaling system comarranged for communication over a high voltage transmission line 10. vBy 'highvoltage. transmission line is to be understood any system or network of conductors .for the electrical transmission of power over which it is possible to transmit high vfrequency waves.

The repeater, shown in Figs'. 3 and 4, serves to repeat calling signals and telephone conversations past a discontinuity in the power line 10, such as a voltage transformer or open power switch 11. Stations A and B are connected to the power line at the left of the repeater, and stations C and D are connected to the power line at the right of the repeater. Each station is equipped with terminal apparatus similar in arrangement and function to that shown at station A in Figs. 1 and 2. The following description of station A, which is also representative of the other stations, will be vfollowed by a description of the repeater and a consideration of the method of communicating between the several stations.

Station A.

The terminal apparatus at station A comprises an outgoing channel and anincoming channel which are connected to the power line 10 by means ofa coupling circuit 12. This coupling circuit may be of thetype disclosed in a copending application of W. V. Wolfe, Serial No. 664,147, filed September 22, 1923, permitting the transfer of high frequency waves between the terminal apparatus and the'power line without danger to the apparatus or the operator.

.High pass and low pass filters 13 and 14 are connected to the coupling circuit 12 and are arranged to be included alternatively in either the outgoing channel or the incoming channel by means of apparatus hereinafter described. These filters, and the other filters employed in the system, may be designed in accordance with the principles set forth in U. S. Patent No. 1,227,113 to` G. A. Campbell, issued May 22, 1917.

Telephone communication with a distant station is effected by means of. an operators telephone set 15 comprising a receiver which is connected to the incoming channel, and a transmitter which is arranged to be connected to the outgoing channel when the receiver is removed from the switchhook. lA selector key 16 controls the transmission of calling signals to the distant stations in a manner hereinafter described. This key may be of any suitable type such as the master impulse transmitting device disclosed in U. S. Patent No. 1,354,814 to J. C. Field, issued October 5, 1920, which may be adjusted to transmit the proper combination of impulses for calling any station on the line. A selector 17 associated with the receiving channel responds to either of two different groups of incoming impulses for controlling the operation of a bell or other signaling device 18. One of the two groups of impulses is used by station B when the operator at station B desires to call station A. The other Group of impulses is used by the repeater oriy stations C and D, which are connected to the power line at the right of the repeater, when the operator at any of these stations desires to call station A. The selector 17 may be of the type disclosed in U. S. Patent No. 1,343,256 to J. C. Field, isi sued June 15, 1920.

The outgoing channel includes (1) an amplifying tube 19 for amplifying the outgoing speech currents; (2) an oscillator 2O designed to produce waves at two different high frequencies, for example, and 100 kilocycles per second; (3) a constant current modulator including the tube 21 and associated circuits 22 to filter 13 or 14 through transformer 25, f

and when thrown to the right connectsthe output circuit of amplifier 22 to the input circuit of auxiliary amplifier 23 through transformer 26, and connects the output circuit ofy auxiliary amplifier 23 to filter 13 or 14 through transformer 27.

It will first be assumed that line conditions are normal and that the auxiliary amplifier 23 is not to be used, in which case the switch 24 is closed in the left position. Filament heating current is supplied to the tubes 19,20, 21 and 22 under the control of a heavy duty relay'30 having a high inductance winding which is adapted to be energized in a manner hereinafter described. The filament heating circuit extends from grounded battery 31,

through the filaments of the tubes, right hand armature and contact of relay 30 to ground. Space current is supplied to the tube 19 through a circuit extending from the positive side of battery 32, through the primary winding of transformer 33, the plate, discharge .path and filament of tube 19, resistances 34 and 35, to the negative side'of battery 32. The current flowing in this circuit produces a drop in. potential across the resistance 34 which causes a negative biasing potential to be impressed upon the grid of tubel 19. The oscillator tube 20 is supplied with spacev current through a circuit extending from the positive side of battery 32, through the primary winding oftransformer 36, the plate, discharge path and filament of tube SU, filaments of tubes 21 and 19, resistances 34, and 35, to the negative side of battery 32. A blocking condenser 37 prevent-s the plate potential from being applied to the grid -of the oscillator tube 20. A condenser 38 which is permanently connected in the oscillator circuit determines the higher carrier frequency of killocycles per second, and the addition of condenser 39 in parallel as shown in the transformer 36 couples the output circuit of oscillator 20 to the amplifier 22 whereby the carrier waves are amplified before being impressed upon the power line.

The carrier waves 1n the anode-cathode circuit of the amplifying tube 22 are modulated according to the constant current method ofniodulation disclosed in a copending application of R. A. Helsing, Serial No. 525,906, filed December 30, 1921. The modulating tube 21 has its plate connected to the plate of the amplifying tube 22 through the primary winding of transformer 25. Space current is supplied to these tubes from the battery 32 through a retard coil 40. The drop in potential across the resistances 34 and 35 due to the current flowing therein causes a negative biasing potential to be impressed upon thel grid of the tube 21. The drop in potential across theresistance 34, which is connected between the filament and grid of the amplifying tube 22, vcauses a negative biasing potential to be impressed upon the grid of this tube. The retard coil 40 offers a high impedance to the speech and carrier currents and hence there will be no change in current through this coil. Speech variations which are impressed upon the grid of the modulating tube 21, however, produce variations in the impedance of the anode-cathode circuit of this tube. The condenser 41 serves to bypass the carrier current around the retard coil 40, but offers an impedance such that changes in the impedance of the anode-cathode circuit of the modulating tube 21 produce corresponding changes in the carrier current fiowing in the anode-cathode circuit of the amplifying tube 22. As a result of this action the carrier waves flowing in the output circuit of the amplifying tube 22 are modulated in accordance with the speech variations which are impressed upon the grid of themodulating tube. 21. Both the upper and lower side bands produced by modulation are impressed upon the power line along with a component of carrier frequency. The condenser 42 serves to by-pass speech frequency currents in the output circuit -of tube 19 around resista ces 34 and 35. Condenser 43 byepasscs alte nating currents around the plate battery 32, and condenser 44 ley-passes alternating currents around the filament batterv 31.

1f line conditions are bad owing, for example. to a section of the line being down, 'the switch 24 is moved from the normal left position to the rightposition. The plates of the modulating and amplifying tubes 21 and 22 are then connected together through the primary winding of transformer 26pinstead of through the primary winding of transformer 25. The production and modulation of the carrier waves, however, is accomplished in the manner described above. Filament heating current is supplied to the aux'- iliary amplifying tube 23 over a circuit extending from grounded battery 45, through the filament of tube 23, switch 24, left hand armature and contact of relay 30, 'to groundf Space current is supplied to the tube 23 over a circuit extending from the positive side of battery `46, through the primary Winding of transformer 27, the plate, discharge path and filament of'tube 23, resistance 47 to the negative side of battery 46. The current flowing in this circuit produces a drop in potential across the resistance 47 which causes a negativebiasing potential to be impressed upon the grid of the tube 23. The condensers 48 and 49 vserve to by-pass alternating currents around battery 46 and'resistance 47 respectively. When the auxiliary amplifier 23 is connected in circuit, thde amplified carrier and side band waves are transmitted through the transformer 27, filter 13 or 14, as the case i maybe, and coupling circuit 12 to the power l line 1U.- y l The incoming channel extends from the power line 10, through the coupling circuit 12, to the high pass or low pass filter 13 or 14, and includes in addition to these elements, (1) a common collecting circuit 51 for receiving unmodulated carrier waves, carrier waves interrupted in accordance with the calling impulses, and the side bands representing the carrier waves modulated in accordance with speech; (2) an amplier 52 for amplifying the received calling impulses; (3) a rectifier 53 for rectifying the amplified calling impulses; (4) a demodulator 54 for combining grounded filament of tube 52. Space current is supplied to the rectifying tube S3-through aA circuit extending from grounded battery 60, through the winding of relay 62, the plate, discharge path and grounded filament of tube 53. The grid of the amplifying tube 52 is made negative with respect to the negative end `of its filament'due to the drop in potential produced by the filament current in resistance 59. The-grid of the rectifying tube-53 is made negative with respect to the negative end of its filament due to the drop in potential produced bv the filamentcurrent in resistances 58 and 59 and the filament of the amplifying tube 52. The relay 62 is a marators telephone set 15.

selector 17, as hereinafter more fully ginal relay and 'is not operated by the small current normally flowing in the anode-cathode circuit of the rectifylng tube 53 when no calling impulses are received. The characteristics of the ytube 53 and its associated circuits are such that the received calling impulses of carrier frequency are rectified and caused to operate the relay 62. The operation of this relay causes the stepping up of the described. The condenser 63 by-passes the alternating current in the output circuit of the tube 53. The condenser 64 ley-passes alternating currents around the winding of relay 62.

The demodulating and amplifying tubes 54 and 55 are supplied with filament heating current through a circuit extending from the negative side of battery 65, through resi-stances 66, 67 and 68, the filaments of the tubes,

to the positive side of battery 65. Space cur-- rent is supplied to the tube 54 over a circuit extending from grounded battery 60, through the primary winding of transformer 69, the plate, discharge path and grounded filament of tube 54. Space current is supplied to the tube 55 over a circuit extending from ground-v ed battery (30, through the primary winding of transformer 70, the plate, discharge path and grounded filament of tube 55. The grid of the tube 54 is made nega-tive with respect to the negative end of its filament due to the drop in potential produced by the filament current in resistances 67 and 68 and the filament of tube 55. l The grid of the tube 55 is made negative with respect to the negative end of its filament due to the drop in potential produced by the filament current in resistance k68. Again control potentiometer 71 is included in the input circuit of the demodulator tube 54.' A condenser 72 in the output circuit of tube 54`serves to by-pass the high frequency carrier waves. The speech frequency` waves in the output circuit of the demodulator 54 are amplified by the amplifier 55 and transmitted through transformer 70, low pass filter 7 3, resistance network 74, and transformer 75 to the receiver of the opery The low pass filter 73 is designed to pass waves comprised within the speech frequency range and to suppress waves of other frequencies.

Repeater.

T he repeater, shown in lFigs. 3 and 4, comprises anoutgoing channel and an incoming channel which are connected to the power line 10 on both sides of the voltage transformer or upon power switch A11 by means of coupling circuits 112. r1`hese coupling circuits are similar to the coupling circuit 12 employed at station A. l The repeater is arranged to receive only waves of 100 and 11() kilocycles frequency and to transmit only waves of kilocycles frequency, the high pass filter 113 being permanently connected f to the incoming channel and the low pass filter 114 being permanently connected to the outgoing channel.

Telephone communication with a distant terminal station is effected by means of an operators telephone set 115 comprising a receiver which is connected to the incoming channel, and a transmitter which is arranged to be connected to the outgoing channel in a manner hereinafter described. A selector key 116 is employed to transmit calling signais when the operator at the repeater desires to communicate with the operator at any station. A selector 117 associated with the receiving channel is operated according to a predetermined code of impulses when any station calls the repeater. This selector controls the operation of the bell or other signaling device 118. An auxiliary selector 110, having its windings connected in parallel with the windings of selector 117, is arranged to close a contact whenever one station calls another station located on the same side of the repeater. The closure of such contact serves to disconnect the repeater from the talking circuit, as hereinafterl described, so that thereafter the calling and called stations on the same side of the repeater may converse directly without using the repeater. The selector 110 is th-erefore provided with four contacts, one for each station in the system, each of these contacts corresponding in its code setting to one of the selector contacts at a station. As pointed out above, one group of impulses is used when any station is being called by another station on the same side of the repeater, and another group 'of impulses is used when the same station is being called 17 at station A to close its second contact butl does cause the selector at the repeater to close a contact, and hence the repeater' remains in service to repeat the two-way conversation between station A and, station C or D, as the case may be. It will thus be seen that the selector 110 at the repeater is selectively operated only when the calling and the 4called stations arev located on the same side of the repeater.

.The outgoing and incoming 'channels at` the repeater are similar to the corresponding channels at station A and, therefore, will not be described in detail except so far as it is considered necessary to understand the operation of the system. .The outgoing chanfrequency amplifier y relay 6, winding of relay 79, to ground. Re-

nel includes a speech 119, an'oscillator 120, amodulator 121, 'an amplifier 122, and an auxiliary amplifier 123 which may .be connected, to or disconnected from the circuit by' means of switch 124.

\The condensers 138 and 139, which are normally connected in parallel in the oscillator circuit, determine the carrier frequencyv ,of 80 kilocycles per second assigned to the outgoing channel. The disconnection of con-V denser 139 from the circuit in accordance with groups of impulses permits corresponding groups of impulses of 80 kilocycles frequency to be transmitted through the low pass filter 114 to the line.

The incoming channel includes lan amplier 152 for amplifying the received calling impulses, a rectifier 153 for rectifying these impulses, a demodulator 154 for demodulating the received speech modulated carrier Waves, and an amplifier 155 for amplifying the speech currents. It Will be noted that space current from the source 160 is supplied to the rectifier tube 153 through the Winding of relay 162. This relay is marginal, like the relay 62 at station A, and is operated only in response to the rectified current flowing in the anode-cathode circuit of the rectifier tube 153. f

@ailing and tal/sing throng/t repeater.

In describ-ing the operation of the system, the method of calling and talking through the repeater from station A to station D Wlll first be considered. The arrangement of the carrier frequencies transmitted and received by the different stations in this situation is illustrated in Fig. 5a. Stations A and B, as pointed out above, are capable of transmitting or receiving carrier Waves of .80 and 100 kilocycles frequency, depending upon the arrangement of the terminal filters. Stations C and D, on the opposite side of the repeater, are capable of transmitting or receiving carrier waves of 80 and 110 kilocycles frequency, depending upon the arrangement of the lters at these stations. in the operation of the system first to be considered, it is to be understood that the system is functioning in its normal condition, that is, there is no line failure, and the repeater Will function to repeat signals between the several stations. Under such condition the key 77 at station Ait, and all the other stations is closed. The

key 77 is never opened until it has been definitely determined that the repeater Will-not vreceive a call.

lThe operator at station A, in initiating a call to station D, removes his receiver from the switchhook, thereby operating relayA 76 over a circuit extending from grounded batl tery 78, through the lower contact of the switchhook, Winding of relay 76, to ground.

Relay 79 is thereupon energized over a circuit extending from grounded battery 80, throu h the front contact and armature of lay 81 is energlzed over ya circuit extending from grounded battery 80 through the front contact and armature 7 6', key 77, Winding of relay 81, back contact and armature 'of relay 82, to ground. The operation of relay 81 causes the energization of relay 83 over a circuit extending from grounded battery 84, through the winding of relay 83, uppermost front contactand armature of relay 81, to ground. The operation of relay 79 causes the operation of relay 30 over a circuit which extends from grounded battery 85, through the uppermost armature and contact of relay 79, Winding of relay 30, to ground. The condenser 86 and resistance 87 serve to protect the upper contact of relay 79 against sparking due to the high inductance ofthe Winding of relay 30. The energization of relay 30 causes filament heatin vcurrent to be supplied to all the space disciiarge tubes in the out oing channel, including the auxiliary ampli ying tube 23, if this tube' is in service. The filament circuits were traced above in the description of the terminal apparatus.

Relay 83, in operating, opens its lowermost contact, thereby preventing relays 88- and 89 from being energized through this contact and the first lower contact and armature of relay 79. The relays 88 and 89y control the connections of the high pass lilter 13 and-the low pass lter 14, and by maintaining these relays deenergized, the high pass filter 13 remains connected to the outgoing channel and the low pass filter 14 remains connected to the incoming channel, as shown in the drawings. Relay 90 is normally energized over acircuit extending from grounded battery 92, through the Winding of relay 93, resistance95, second upper armature and back contact of relay 83, Winding of relay 99, uppermost back contact and armature of relay 81 to ground, the cur-A rent flowing in this circuit, however, being insufiicient to operate the relay 93. rll'aeoperation of relay 81 opens the energizing circuit of relay 90. Furthermore, the relay 81, in. operating, attracts its'rst lower armature, thereby vpreparing a circuit to be closed through the relay 90, grounded battery 91and selector ke 16l When the selector key 16 is subsequent y operated. At the same time, relay 81 attracts its lowermost: armature, thereby preparing a circuitto be closed through grounded battery 92, pole changing' relay 93 and selector key 16 when the selector key 16 is subsequently operated. As a result y v13 and coupling circuit 12 to the power line 10.

vCarrier waves of this frequency, however,

will not'pass into the receiving'cha'nnel at station B which, like the receiving channel at station A, is' normally arranged to receive.

only waves of 80 kilocycles frequency. The carrier waves received in the cirfcuit 151 .at the' repeater are amplified by the amplifier 152 and rectified by the rectifier 153, the rectilied waves causing the operation of relay 162. The operation of relay 162 causes the oper'ation of relay 174 over a circuit extending from grounded battery'175, through the contact and armature of relay 162, winding of relay 174, to ground. Slow releasing relayy 176 4is also operated over a circuit yextending from grounded battery 17 5, through the contact and armature of relay 162, winding of relay 176, to ground. vThe relay 177 which controls the connection of the, condenser 139 "to the circuit of the oscillator 120 is normallyenergized over a circuit extending from grounded battery 178, through the winding of polechanging relay 179, resistance 180,

upper middle armature and contactof relay f 181, winding of relay 177, to ground, the current flowing in this circuit, however, being insufii'cient to operate the relay 179. `The operation ofrrelay 174 completes another energizing circuit for the relay 17 7 which extends from grounded battery 182, through the uppermost armature and contact of relay 174, winding of relay 177, to ground.L The operation of relay 174 also causes the operation of relay 179 over a. circuit extending from grounded battery 178, through the w-inding of relay 179, middle armature Vand contact of relay 174, to ground. The operation`of relay 179 causes an imf-pulse of current from` the source 132 to be supplied to the electrbmagnets of selectors 110 and 117. The selectors will thereupon advance one step but will immediately fall back to the starting position. If either of these selectors happens accidentally to be held in an advanced position before the call is initiated, this single impulse will cause it to advance another ste to a position from which it will promptly vall back to the normal starting position before the operator at station A actuates his calling key 16. The relay 174 in attracting its lowermost armature opens a shunt path around the relay 162 which would otherwise be closed upon the operation of relay 183, and would extend from grounded battery 160, through the upper armature and contact of operation vof slow releasing relay 184 causes the energizatioii of relay 181 over a circuit extending from grounded battery 186, through the winding of relay 181, armature and contact of relay 184, to ground. Relay 181 in opening its uppermost contact opens the shunt path around the relay 162 which was traced above. lBy opening its second upper contact the relay 181 opens the energizing circuit of relay 177 which extends throughl resistance 180, the relay 177, however, remaining energized over the circuit previously tracedl from grounded battery 182 through the uppermost armature of relay 174. lThe relay 181 also closes its third upper contact,

establishing an energizing.' circuit for relay l 183, which extends from grounded battery 187 ,Y through the third upper armature and contact of relay 181, winding of relay 183,.to

ground. At its lowermost contact the relay 1 81 opens a circuit through the relay 190 so that thisvrelay will remain deenergized even if the operator at the'repeater removes his Areceiver from the switchhook. The operation of relay 183 establishes an energizing circuit forrelay 130, which may be traced from grounded battery 188, through the lower armature and contact of relay 183, upper arma ture and contact of relay 189, winding. of relay 130, toground. The operation of relay 180 causes filament heating current to besupplied to all the space discharge tubes in the y outgoing channel, including the auxiliary amplifying tube 123 if this tube is in servico. Carrier waves of 80 kilocycles frequency generated by the oscillator' 120 are thereupon transmitted througlrthe low pass filter 114 and coupling circuits 112 to both sections of the' power line 10. These carrier waves of 8O kilocycles frequency are received by all the sta- I tions, and are rectified at stat-ions B, C and D and caused to operate the relay thereat which corresponds to'relay 62 at station A. While the relay 62 at station A also operates in responseto these 80 ki'locyclewaves, it performs no useful function at this time. The

circuits 'controlled by. this relay are already energized. The operation of such relay at stations B, C and D, however, causes the selector at each of these stations toadvance one step from which advanced position it will fall back to the starting position.

The sequence'of operations described above took place when the operator at station A removed his receiver from the switchhook. The operator at station -A now actuatesthe selector-key `16 which is set to transmit the pro er combination of. impulses for calling station D. vThe operation of selector ukey 16 causes the relay 90 to operate each time a tooth of the selector key closes the key contact. The energizing circuit of the relay 90 may be traced from ground, through the closed contact 'of selector key 16, lowermost armature and front contact of relay 81, winding of relay'90, first lower contact and armature of relay 81, resistance 94, to grounded battery 91. The alternate energization and deenergization of rela 90 in response to these impulses causes t e condenser 39 to be placed alternately into and out of the oscil` lator'circuit. During the operation of the selector key the frequency generated by the oscillator 2O is thus changed back and forth lfrom the high carrier frequency of 100 kilofrequency of 100 kilocycles per second are CTI thus transmitted to and impressed upon the power line. The operation of the selector key lalso completes lanenergizing circuit for the pole changing relay 93, from grounded'A battery 92, through the winding of relay 93,;resistance 95, second upper armature andA front Contact of relay 83, lowermost front contact and armatureof relay 81, closed con'- tact of selector key 16, to ground. The energization of-relay 93 causes the impulse of cur`' rent from the battery 32 to be .supplied 4to the electromagnet of selector 17 which causes the selector to advance one step.` l/Vhen the contact of the selector key is opened, the relay 93 releases, which causes an impulse of currentfofopposite sign through the electromagnet orl selector 17. The operation of relay 93 and the selector 17 at thisI time performsl no useful function, but is usually provided for in systems of this general type so that relay 93 may also be used to relay calling impulses to a sub-station, not shown i the drawing, if this feature should be found desir'able. n y

rllhe high frequency impulses which `are transmitted over the power line pass through the left hand coupling circuit 112 at the repeater, and thence through high pass filter 113 to the common collecting circuit 151, amplifier 152 and rectifier 153. The rectified impulses in the output circuit of the rectifier 153 cause the alternate 'deenergization and` energization of Ielayf 162, thus alternately opening and closing the energizing circuit of relay 174 which, in turn, causes the relay 177 to release and operate, alternately placing the condenser 139 out of and into the circuit of oscillator 120.l As a result of this action groups of impulses of kilocycles frequency, corresponding in number and. arrangement to the impulses transmitted from station A, are transmitted through.low pass filter 114 and couplin circuits 112, to both sections of the power l1ne.. The relay 174, in opening and closing its first lower contact, alternately opens andcloses the energizing circuit of relay179, thereby causing selectors 110 and 117 toy advance stepby-step. The relays 176 and 184 at the repeater are made slow releasing in order to maint-ain the relay 181 energize'd during the calling operation, thus maintaining the closure of the filament circuit of the tubes in the outgoing channel. The

relay 190, lbeing unoperated, maintains the closure between the incoming and the outgoing repeater channels through Which the speech currents are to be transmitted. The calling impulses of 80 kilocycles frequency which are relayed from the repeater cause the selectors at stations B, C and D to step up, but only the selector at station D closes the proper contact.` T-he selectors at the repeater and the other stations fall back to the starting position. The operation at station D-may be followed by referring to the corresponding apparatus at station A, shown in Figs. 1 and 2. The alternate energization and deenergization of relay 62 at station D- in,

relay 83, the circuit of relay 83 extending from grounded battery 84, through the winding of relay 83, armature and contact of relay 62, to ground.- The intermittent operation ofi relay 83 by relay 62 causes the intermittent operation of the pole changing relay 93.

`The energizing circuit of relay 93 extends from grounded battery 92, through the winding of relay 93,l resistance 95, second upper armature and front contact of relay `83, upper most back Contact andarmature of relay 81, to ground. The operation of relay 93fcauses the selector 17 to step up until it closesthe contact corresponding to the transmitted code of impulses. When the selector 17 at station D stops at the proper contact, .n

the relay 96 is energized'ove a circuit extending from grounded battery 97through the upper windingof relay 96, closed contact of selector 17, to ground. Relay 96 is thereupon locked up through a circuit extending from grounded battery 80, through the back contact of relay 76, lower winding and armature of relay 96, to ground. The bell 18 is energized over a circuit extending from grounded `battery 98, through the electromagnet of bell 18, lower contact and armature of relay 96, i

to ground. It will be noted that the contact line.

of selector key 16 at the calling station -A is opened at thel conclusion of the dialing, that is,tliis Contact is opened after the last tooth has passed the contact arm of the selector key, and as a result carrier waves of 100 kilocycles frequency continue to flow from the outgoing channel at station A to the power quency are therefore impressed upon the power line from the outgoing channel of the repeater at the' conclusion of the dialing op eration. The carrier waves of 80 kilocycles 'frequency which are thus received at station L maintain the relays 62 and 83 energized during the subsequent communicationbetween stations A and D. The final operation of relay 83 causes an additional impulse through the pole changing relay. 93 which causes the selector 17 to advance another step from which advanced position it falls back to the starting position.

W'hen the operator atstation D. responds to the call by lifting his receiver from the switchhook, the'relay`7 6 is operated over the` circuit previouslytraced. Relay 76 establishes energizing circuits forrelays 7,9 and 81, which were traced above in describing the operation at station A. Relay 7 9 in attracting its uppermost armature, causes the operation of relay 30 which lights the filaments ofl the space discharge tubes in the outgoing channel atstation D, causing carrier waves of 110 kilocycles frequency to be impressed upon the power line. The operation of relay 76 also opens the locking vcircuit of relay 96 thereby deenergizing the bell 18. Relay 81 which, in operating, establishes an energizing circuit for relay 83, actually performs nol useful function at this time since relay 83 is already energized through the closed contact of relay 62. rllhe energization of relay 83, it will be noted, prevents relays 88y and 89 froml operating since the energizing circuits of these relays are' open at the lowermost contact of relay 83." Accordingly, the outgoing channel at station D is arranged to transmit carrier waves of 110 kilocycles frequency andv the incoming channel at stationD is arranged to receive carrier waves of kilocycles fre-- quency.

Speech modulated carrier waves of 100 kilocycles frenency impressed upon the power line at station A pass through the left hand coupling circuit 112 at the repeater, and thence through high pass filter 113 to the common collecting circuit 151. These waves are combined in the demodulator 154 with the unmodulated carrier component which is also transmitted over the line. The low freq-uency components of demodulation appearing in the output of the demodulator 154 are amplified by the amplifier 155 and transmitted through low. pass filter 173, resistance network 191, back contacts and armatures of relay 190, to the input circuit of speech Carrier waves of 80 kilocycles fre-- the switchhooks,causing.thesystem to refrequency amplifier 119.- The speech cui'- rents which are thus supplied to the outgoing repeater channelare caused to modulate the carrier waves of 80 kilocycles frequencyproduced by thep'scillator 120, and the modu- 7n lated carrier'w'avesare transmitted over thef power line to station D. A portion of the waves received at the repeater is rectified to maintain the relay 162 energized. Similarly, the speech modulated carrier waves of 110 kilocycles frequency impressed upon the power line at station D aref'transmitted to the repeater where they are converted into speech modulated carrier waves of 80 kilocycles frequency which are transmitted to station A. At station A these waves are demodulated in the demodulator 54 and the low frequency components of demodula'tion, after being amplified by amplifier 55, pass through low pass filter 73, resistance' network 74 and transformer 75 to the receiver ofthe operatorsl telephone set 15'. Upon the completion of the conversation, the operators at stations 4 'A and D will replacev their receivers upon v turn tothenormal condition shown in the drawings... On a callthrough the repeater,l such as that described above, the receiver associated with the operators telephone set '115 is connected to the talking circuit so that the operator at the repeater may determine when A the line is busy. If, however, the operatorat p the'repeater should dial under this condition, the dialing` will be ineffective,.since.the circuit extending from the 'selector key 116 to 100 the relay v177 is openat the second upper armature and contact of relay 181.

`.UaZZag mil tal/ring to repeater.

When vthe operator at'station A desires to 105 call and converse with the operator at the repeater, he proceeds in the manner employed in calling station D exceptthat the selector key 16 vmust first be adj usted to transmit the particular code of impulses which will cause the selector 117 at the repeater to. close its associated contact. When such a call has beenl initiated at station A, the operation of the .apparatus at station A and the repeater .is

the same as thatv previouslyv described up to the stepping up ofthe selectors in response to the calling impulses. Only the selector 117 at the repeater stops-on thegproper contact, the selector. 110 and the selectors at the several stations falling back to the starting position. The operation of selector 117 causes the energization of relays 193 over a circuit extending from grounded battery c 194, through the lower winding of relay 193, closed contact of selector 117, to ground. A holding circuit for relay 193 is established from grounded battery 195, through the lower armature and contact of relay 196, upper i winding and uppermost contact and armature of relay 193, to ground. -An energizing 130.

conclusion of the calling impulses cause the selector 117 to advance a linal step from which advanced position it falls back to the starting point. The relay 190 is energized over a circuit extending from grounded battery 186, through theffirst lower armature and contact of relay 181, which was energized by relay 184 in the manner previously described, lowermost contact' and armature of relay 193, contact 197 of relay 190, winding of relay 190 to ground. vAn energizing circuit for relay 190 is thereupon established from grounded battery 186, through the first lower armature and cont-act of relay 181, lowermost armature and contact of relay 190, winding of relay 190, to ground, so that relay 190 will remain energized even though relay 193 becomes deenergized when the operator removes his receiver from the switchhook. The operationof relay 190 opens the connection between the incoming and outgoing channels of the repeater and connects the. local transmitting circuit of the operators A telephone set 115 to the input circuit of the speech frequency amplifier 119. When the operator removes the receiver from the switchhook, the local circuit of the operators transmitter is closed, and the relay 196 is energized over a circuit extending from grounded battery 198, through the lower contact of the switchhook, winding of relay 196, to ground. Relay 196 in opening its lower contact ,breaks the holding circuit of relay 193, thereby deenergizing the bell 118. A second energizing circuit is established for the relay 183 from grounded battery 195, through the upper armature and contact of relay 196, winding of relay 183 to ground, which, however, performs no useful function at this time, since the relay 183 isalready energized over a. circuit previously traced through the third upper armature and contact of relay 181. The circuit from grounded battery 195 through relay 183, however, is the circuit which is established for operating the relay 183 to energiz the lilaments of the space discharge tubes insthe out-going channel when a call is init-iated'at the repeater. The operators at station A and the repeater may now converse, station A transmitting' at 100 kilocycles and receiving at 80 kilocycles, and the repeater transmitting at 8O kilocycles and re- 'ceiving at 100 kilocycles, as indicated in Fig. 5b.

aZZzng and talking to station, on same side of repeater.

The operation of the system on a call undernormal line conditions from station A through the repeater to stationB willnow be described. In this situation, as in the situations described above, the key 77 at station A remains closed.` The operator at station A proceeds to call station B in the manner employed in calling either station D or the repeater, except that the selector key 16 must first be adjusted to transmit the particular combination of impulses which will cause the selector 17 at station B to close its associated contact. When such a call has been initiated at station A, the operation of the apparatus at station A and the repeater is the same as that previously describedQ up to the stepping up of the selectors in response to the calling impulses. The combination of impulses transl mitted in this case, however, not only cause the selector at station B to close its associated contact, but also cause the selector 110 at the repeater to close one of its four contacts. This is due to the fact that, as pointed out above, one of the contacts of selector 110 corresponds to the code employed by the operator at station A to call station The operation of the apparatus at station B is the same as that previously described in connection with station D up to the completion ofthe dialing. In other words, the calling impulses relayed to station B by the repeater, cause the operation of relays 62', 83 and 93. When the selector 17 at station B closes the proper contact, the relay 96 is operated in the man-ner described above, thereby energizing the bell 18. Although the selector 17 at station B falls back to its starting position, the bell 18 continues to ring until the operator at station B removes his receiver from the switchhook, since relay 96 is llocked up in the manner previousl described.

When the selector 110 at t e repeater closes its associated contact correspondingto the code setting ofthe selector 17 at station B, the relay 189 is operated overa circuit extending from grounded battery 199, through the winding of relay 189, closed contact of selector 110, to ground. Although the selector falls ,back to the starting position, the relay 1895 remains energized over a holding circuit extending from grounded battery 199, ,through the winding, lower contact and armature of relay 189, upper armature and contact of relay 184,'to ground. The relay 189, in attracting its upper armature, opens the energizing circuit of relay 130,' thereby disconnecting battery from the lilaments ofthe space discharge tubes in 'the outgoingchanhel at the repeater. The carrier waves of 80 kilocycles frequency thereupon cease to flow to the'd power line from rthe repeater, and hence relay 62 at station B is deenergized. Relay 62, in opening its contact, opens the energizing circuit of relay 83. `Relay 83 in releasing, and relay 79 in operating as vit does when the operator removes the receiver from the switchhook, short-circuits relay 62 through the second lower armature and contact of relay 79 and the uppermost armature and contact of relay 83, preventing the subsequent Aopera-- tion of relay 62 in response to incoming carrier waves.

When the operator at station B removes his receiver from theswitchhook, the relay 76 is energized, thereby energizing relay 79 overa circuit previously traced from grounded battery 80, through the front contact and armature of relay 76, winding of relay 79,' to ground. The operation of relay 79 causes the energization .of relay which lights' the filaments of the spacedischarge tubes in the outgoin channel. tion removed his receiver from the switchhook, relay 82 was energized over a circuit eX- tending from grounded battery 97, through the second upper contact and armature of re'- lay 96, upper winding of relay 82, lowermost contact and armatureof relay 83, to ground.

. Thereafter when relay 76' was energized upon removing thereceiver from the switchhook, a holding circuit was established for relay 82, from grounded battery 80, through the front contact and armature of relay 76, lower wind- 'ing and the closed contact and armature of relay 82, to'ground. Relay 82 thus remains energized even after relay 96 is deenergized when the'receiver is removed from the switchhook. Relay 82, in attracting its armature, opens the energizing circuit of relay 81. During the transmission of the calling impulses,

- station A, which originates the call, transmits at 100 kilocycles and thev repeater receives at 100 kilocycles and transmits at 80 kilocycles, while all of the other stations receive the in- Jerrupted 8() kilocycle waves, as illustrated in The filter controlling relays 88 and 89 are now energized, the energizing circuit of relay 88 extending from grounded battery 99,

through the winding of relay 88, first lower contact and armature of relay 79', lower armature and contact of relay 83, to ground, and

the energizing circuit of relay 89' extending from grounded battery 100, through the winding of relay 89, first lower contact and armature of relay 79, lower contact and armature of relay 83, to ground. The operation of relay 88 serves to disconnect the high pass filter f 13 from the outgoing channel and connect it totheincoming channel, andthe operation of relay 89 serves to disconnect the low pass filter 14 from the incoming channel and connect it to the outgoing channel. Relay 90 at st-ation B is now energized over a'circuit exv vtending from grounded battery 92, through the winding-of relay 93, resistance 95, second upvper armature and back contact of relay 83,

winding of relay 90, uppermost back contact and armature of relay 81, ,to ground.- Since relay 90 is energized, the condenser 39 is conf nected in the circuit of the oscillator 20 and hence carrier waves of 80 kilocycles frequency are transmitted through low pass filter Before the operator at sta 14 and coupling circuit 12 to the power line 10. The speech modulated carrier lwaves of 100 kilocycles frequency which are impressed upon the ower line at station A pass through the coupllng circuit 12 at station B and are selectively passed bythe high pass filter 13 to the common collecting circuit 51, and are then demodulated in the demodulator 54. The low frequency components of demodulation appearing in the output circuit of the demodulator 54 are amplified by the amplifier 55 and passed through transformer 70, lowT pass filter 73, resistance network 74, and transformer to the receiver of the operators telephone set 15. Although a portionv of the carrier waves received at station D are rectified by the rectif fier 53,- the relay 62 will not operate since the winding of this relay is short-circuited in the manner described above. The operators at stations A and B may thus converse directly without using the repeater, station A 'transmitting at 100 kilocycles and receiving'at 80 kilocycles, and station Bv transmitting at kilocycles and receiving at 100 kilocycles, as indicated in Fig.v 5d.

Calling aml talking to station. on same side of repeater lupon fallar/'e of the line or the repeater.

According to this invention, calling signals and speech modulated carrier waves may be transmitted between two stations which are located on the same side of a 4break in the power line, or on the same side of the repeater, if the repeater fails to operate. For the purpose of illustration it will be assumed that a break has occurred in the power line at some point between station B and the repeater, or

it may be assumed that the repeater has'for some reasonlbeen rendered inoperative. When, this condition prevails, the operator at station A, for example, may nevertheless call and converse with the operator at station B by-first operatingthe key 77. This I key is operated only at-the station which originates the call, in this case station A, and is employed only when it has been determined that the repeater, for either of the reasons mentioned above, will not receive the calling impulses.

The operator at station A, after opening lll) the'key 77, removes his receiver from the lower Contact and armature of relay 79 and the lower contact and armature of relay 83. The operation of relay '88 disconnects the high pass filter 13 from the'outgoin'g channel and connects it to the incoming channel, and the operation of relay 89 disconnects the low pass filter 14 from the incoming channel and connects it to the outgoing channel. Be-

lay 90 remains energized through the circuit previously traced from grounded battery 92,

to ground at the upper back contact andarmature of relay 81. Carrier Waves of 80 kilocycles frequency generated by the oscilla- 'tor 20 are thereupon transmittedA to and im- 15 pressed upon the power line at station A.

The operator at station A novi7 actua-tes the selector key 16'Which; of course, is adjusted to transmit the proper code of impulses for calling station B. The operation of the se? lector 16 causes relay 90 to release and operate alternately, this relay being short-circuited from ground at the contact of the selector key to ground at the upper back contact and ar` mature of relay 81 each time a tooth of the selector key actuates theassociated contact arm. The operation of relay 90 in alternatelyplacing the condenser 39 qut of and into the oscillator circuit causes impulses of 80 kilocycles frequency .to pass through the 10W pass filter 14 and coupling circuit l2 to the'poWer line. Relay 93 and selector 17 at station A also operate, but perform no luseful function at this time.

The opera-tion of the apparatus at sta-A modulated carrier Waves of 8O kilocycles frequency Which are impressed upon-the power line at station A pass'through the coupling circuit 12 at station B and are selectively passed by the low pass filter 14 to the common collecting circuit 51, and are then demodulated in the demodulator 54. Ilie low fre# quency components of demodulation are transmitted to the receiver of the operators telephone set 15 in the manner described above. The operators at stations A and B may thus converse directly Withouthaving used the repeater at all, station A transmiti ting at 80 kilocycles and receiving at 100 kilocycles, and station B transmitting at 100 kilocycles and receiving at `80 kilocycles, as indicated in Fig. 5?. Although a portion of the carrier Waves which are now received at station A is rectified bythe rectifier 53 thereat, the:l relay 62 vWill not operate since the Winding of this relay is short-circuited through the second lower Contact and armature of relay 79 and the uppermost/armature and con-y tact of relay 83. Stations C and D, located on the opposite side of the repeater, may like- Wise communicate with-each other in this manner While another portion of the `system is out of service.-

The invention is capable of other modifica! tions and adaptations not specifically described but included Within the scope of the appended claims.

What is claimed is:

1. Ay transmission system comprising a transmission line, a plurality of stations and a repeater connected to said line, means at each of said stations for transmitting calling signals over said line receivable only by said repeater, means at said repeater responsive to said received vsignals for transmitting over said line signals receivable by said stations, and means at one or more of said stations for transmitting calling signals over said line receivable by other of said stations.

2. A transmission system comprising a transmission line, a plurality of stations and a repeater connected to said line, means at each of said stations for transmitting carrier Waves of a frequency receivable only by said repeater, means at said repeater responsive to said received carrier Waves for transmitting Waves of a-frequency receivable by said stations, andmeans at one or more of said stations for transmitting carrier Waves over said line of a different frequency'receivable by otherof said stations. Y y

3.. A transmission system comprising a transmission line, a plurality of stations and a repeater connected to said line, outgoing and incoming circuits at each of said stations including apparatus for transmitting Waves of one "frequency and receiving'waves of another frequency, means at said repeater responsive to Waves of said first mentioned frequency for transmitting Waves of said second'mentioned frequency, and means operative upon initiating a call at one or more of 4said stations to interchange ltheftransniitting and receiving apparatus thereat with respect to the outgoing and incoming circuits.

4. A transmission system comprisingV two line sections, a plurality of stations connected to each line section, a repeater connecting said line sections, means at each of said sta-4 tions for transmitting calling signals receivable only by said repeater, means at said repeater responsive to received signals for transmitting Waves receivable by the stations connected to each line section, and means at one or more of said stations for transmitting calling signals receivable by other of said stations connected to the same line section.

5. A transmission system comprising two' line sections, aplurality of stations connectedto each line section, a repeater connecting /said line sections, means at each of said stations for transmitting calling signals ofa frequency receivable only by said repeater'. means at said repeater responsive to received signals for transmitting signals ofy au frequency receivableby the stations connected to each line section, and means at each of said stations for transmitting calling signals of a frequency receivable by other of said stations connected to the same line section.

6. A transmission systemv comprising two line sections,'a plurality of stations connected Ato each line section, a repeater connecting said line sections, means at the stations connected to one of said line sections for transmitting carrier waves modulated in accordance with signals, kmeans at the stations connected to the other of said line sections for transmitting carrier waves of diiferent`fre-- quency modulated` in accordance with sig nals,I

means at-said repeater for retransmitting said signals as modulations of carrier waves of a third frequency receivable by said stations, and switching means operative upon initiating a call at one or more of said sta- Y tions to condition the transmitting means thereat'to transmit signals as modulations of carrier waves of said third frequency.

7.l A transmission system comprising two linesections, a plurality of stations connected to each line section, va repeater connecting said line sections, means at the stations connected to one of said line sections for transmitting waves comprised within one band of frequencies and receiving waves comprised l within a second band of frequencies, means I' waves comprised within the band of frequencies .receivable by other stations connected to the' same line section.

8. A transmission system cqmprising two' line sections, a plurality of`stations connected lto each line section, a repeater connecting said line sections, outgoing and incomin cir-` cuits at the stations connected to one o said line sections'including apparatusfor transmitting .wav s comprised within one band of frequencies nd receiving waves comprised within a second band of frequencies, outgoing and incoming circuits at the stations connected to the other of said line sections including apparatus for transmitting waves compi'ised within a third band of frequencies and receiving waves comprised within said second band of frequencies, outgoing and'incoming circuits at said repeater including apparatus for transmitting waves comprised within said second band of frequencies and receiving waves comprised within said rst and third bands of frequencies, and means operative upon initiating a call at one or more of said stations to interchange the transmitting and receiving apparatus thereat with respect to the outgoing and incoming circuits.

9. A transmission system comprising two line sections adapted for the simultaneous transmission of power currents and signaling`v waves, a plurality of stations associated with at least one of said sections, a repeater connecting said sections, means at one of said stations for transmitting waves of `afrequency receivable only by said repeater, means at said repeater responsive to received waves for transmitting waves of a frequency receivable by said stations, and means at one or more of said stations for transmitting waves of a different frequency receivable by other of said stations. f

l0. A transmission systemnomprising two line sections adapted for the simultaneous transmission of powercugrents and'signaling waves, a pluralityof stations connected to each line section, a re eater connecting said line sections, means or selectively calling any of said stations from any other of said stations through said repeater over said line sections, andl means at each 4of said stations for directly calling the stations connected to the same line section over said line.

11. A transmission system comprising two line sections adapted for the simultaneous transmission of power currents and signaling waves, a plurality of signaling stations connected to each of said line sections, a signal repeater station connecting said line sections, means 'for selectively calling and communicating with any of said stations from any other of said stations through said repeater, and means at each of said stations for di' rectly calling and communicating with the stations connected to the same line section.

12. A transmission system comprising two line'sections adapted for the simultaneous transmission of power currents and-signaling waves, a plurality of signaling stations connected to each of said line sections, a signal repeater station connecting saidline sections, lmeans for selectively calling and communicating with any of said stations from any other of said stations throu h said repeater over said line sections, an means'at each of said stations for directly calling and' communicating ywith the, stations connected to the same line section independently of the repeater. f

i3.v A- carrier wave transmission system comprising a transmission line, a lurality of stations and a repeater connected'to said line, means at each of said stations'for communicating with any other station through said repeater over said line by carrier waves, and means for one of said stations to communicate with any other station by carrier waves over said line vindependently of said repeater. l'

carrier: .wave .transmission system sob iin

comprising two line sections, a-plurality of signal stations connected to each of said 11ne sections, a repeater connecting said line sections, means for selectively eommunicatlng means at each of said stations for directly communicating with any other station conneeted to the same line section by carrier Waves independently of the repeater.

In Witness whereof, I hereunto subscribe my name this 3rd da of February, A. D. 1927 LAW ENCE W. DAVEE. 

